Typo in selector

Author: Martin Durant

setup.py

@@ -90,7 +90,7 @@
                  'Programming Language :: Python :: 3.6',
                  'Programming Language :: Python :: 3.7',
                  'Programming Language :: Python :: 3.8',
-                 'Programming Language :: Python :: 3.9,'
+                 'Programming Language :: Python :: 3.9'
                  ],
     ext_modules=ext_modules,
     packages=packages,